In electronic devices, components, such as the main body, chassis, and heat sinks having heat generating parts are typically produced from metals. The reason for using metals is that metals have a high thermal conductivity. A metal dissipates the heat received very quickly to the surrounding area as compared to other materials. Therefore, metals can maintain electronic parts that are sensitive to heat under high temperature conditions. In addition, metals have high mechanical strength as well as good processing capability in sheet metal machining, stamping, and cutting processes. Therefore, metals are suitable materials for use in heat sinks, the shape of which maybe complex.
It can be difficult, however, to make heat sinks made of metal light weight because of the high density of metal. Moreover, processing costs can be high with metals.
Therefore, thermally conductive materials using synthetic resins have been developed to replace metals. For example, a thermally conductive resin could be used to make heat dissipation sheets or heat dissipation grease on printers, copiers, notebook computers, and the like.
Recently, because of increased demand for high integration and high performance of electronic devices, high amounts of heat are generated inside electronic devices. In addition, electronic devices are becoming thinner or lighter in weight. Therefore, dissipation of heat generated by the devices poses serious problems. Sometimes, serious problems arise in electronic devices due to locally generated heat which ultimately can cause malfunctions or burning of the devices. Thermally conductive resin compositions developed so far have low thermal conductivities, and thus these problems remain unresolved.
If thermally conductive fillers are used in a large amounts to improve the thermal conductivity of the resin composition, the viscosity of the resin composition can increase, which can result in poor fluidity during the molding process. This can make it difficult to produce a product by an injection molding process. Also the strength of the final product may not be satisfactory. For the reasons enumerated above, it is important to form an effective network of fillers inside the resin composition to maximize the thermal conductivity while minimizing the amount of fillers used therein.
A resin with a much lower viscosity can be used so as not to impair the fluidity during injection molding process, even if fillers are added in a large quantity. However, resin with low viscosity has a low molecular weight which can increase the reactivity between the molecular chains during the extrusion or the injection molding process.
Accordingly, it is important to ensure fluidity to form an efficient network of fillers to produce a resin composition having a high thermal conductivity and to allow injection molding. Further, the viscosity of the resin should be reduced and the stability during the process should be maintained.
Typically, carbon or graphite fillers have been used to improve the thermal conductivity of resin compositions. Although these fillers have high thermal conductivity, they also have electrical conductivity and thus cannot be used in applications requiring electrical insulation, such as display or electronic devices.
Inorganic fillers can have high moisture absorbing property. Out-gas release of a resin composition including inorganic filler can increase during injection molding. This can also impair physical properties of the final product.